Infant botulism is a toxicoinfection in which Clostridium botulinum colonizes the gut and produces its neurotoxin. As studied with an infant mouse model, the infection occurs only in infants because of the absence of certain bacteria which are present in the gut of adults and which act as barriers to the multiplication of C. botulinum. The antibotulinum species in the adult will be identified by using germfree mice which are highly susceptible to enteric botulinum infection. Isolates from the colon of conventional adult mice will be fed to the germfree mice, singly or in combinations. If the intragastric challenge with botulinum spores fail to infect the ex-germfree mice, the animals have been associated with an inhibitor of C. botulinum. Spores of several different strains of C. botulinum types A and B will be titrated for ability to intraintestinally infect conventional infant mice (ID50 doses). Enteric botulinum colonization of infant mice does not cause overt botulism or constipation. Reducing gut motibility of infected mice with drugs may result in absorption of toxin being formed in the colon and lead to observable illness.